Determining Shut off Land Relief and Contact Stress in Multi Cavity Tooling
Balancing shut-off land relief area against clamp force prevents steel hobbing while holding plastic melt seal across multi-cavity injection tooling.
Injection Mould Parting Line
Meaning
The geometric boundary where the stationary and moving halves of a tool assembly meet defines the primary shut-off area for the polymer melt. Every injection mould parting line represents a potential location for flash if the tool fit is imperfect or the clamping force is insufficient. Designers place this line to avoid aesthetic interference while ensuring the part can be ejected.
Visual Quality
Witness marks appear on the plastic surface at the point of contact between the steel plates. Careful placement on an edge or hidden surface prevents the injection mould parting line from detracting from the product appearance. This choice is visual.
Venting Function
Gaps of a few microns are ground into the faces to allow air and gases to escape during injection. Without these vents, trapped air causes burn marks and short shots near the end of the flow path. The precision of this gap ensures that gas leaves while the viscous polymer remains contained.
This escape route is necessary.
Ejection Geometry
The position of the split determines the draft angles required for the part to release without dragging. Complex parts may require a stepped injection mould parting line to accommodate undercuts or slides. Simple flat lines are easier to maintain and cheaper to manufacture.
Consistent cleaning of these surfaces prevents debris from creating permanent indentations in the steel.